1. Field of the Invention
The present invention relates to a fuel cell. More particularly, the present invention relates to a separator structure of the fuel cell.
2. Description of Related Art
A PEFC (Polymer Electrolyte Fuel Cell) apparatus includes individual fuel cells. Each fuel cell includes a membrane-electrode assembly (MEA) and a separator. The MEA includes an electrolyte membrane and a pair of electrodes disposed on opposite sides of the electrolyte membrane. The pair of electrodes includes an anode provided on one side of the membrane and constructed of a first catalyst layer and a cathode provided on the other side of the membrane and constructed of a second catalyst layer. A first diffusion layer may be provided between the first catalyst layer and a first separator and a second diffusion layer may be provided between the second catalyst layer and a second separator. The first separator has a passage formed therein for supplying fuel gas (hydrogen) to the anode and the second separator has a passage formed therein for oxidant gas (oxygen, usually, air) to the cathode. A plurality of fuel cells are layered to construct a module. A number of modules are piled, and electrical terminals, electrical insulators, and end plates are disposed at opposite ends of the pile of modules to construct a stack of fuel cells. After tightening the stack of fuel cells between the opposite end plates in a fuel cell stacking direction, the end plates are coupled to a fastening member (for example, a tension plate) extending in a fuel cell stacking direction outside the pile of fuel cells by bolts extending perpendicularly to the fuel cell stacking direction.
In the PEFC, at the anode, hydrogen is changed to positively charged hydrogen ions (i.e., protons) and electrons. The hydrogen ions move through the electrolyte membrane to the cathode where the hydrogen ions react with oxygen supplied and electrons (which are generated at an anode of the adjacent MEA and move to the cathode of the instant MEA through a separator) to form water as follows:
At the anode: H2xe2x86x922H++2exe2x88x92
At the cathode: 2H++2e+(1/2)O2xe2x86x92H2O
To cool the fuel cells, the temperature of which rises due to the heat generated at the water production reaction and a Joulean heat, a cooling water passage is formed at every cell or at every module and a cooling water is caused to flow in the cooling water passage.
International Patent Publication No. WO 96/37920 discloses, at FIG. 11 of the Publication, a fuel cell apparatus constructed of a number of fuel cells layered each including a pair of separators and an MEA sandwiched between the pair of separators. The separator includes a first member and a second member. The second member has a perforation at a portion thereof corresponding to a power generating portion of the fuel cell. The first member has a gas passage portion at a portion thereof corresponding to the power generating portion of the fuel cell. A manifold portion is formed in the first member and the second member, and the manifold portion is offset from the gas passage portion.
However, with the conventional fuel cell, there is the following problem:
Since a reactant gas is supplied to the gas passage portion from the manifold portion offset from the gas passage portion, the gas cannot be supplied uniformly to the gas passage portion. As a result, a high power output cannot be expected at a portion of the gas passage portion where an insufficient amount of gas is supplied, and the fuel cell cannot be operated efficiently.
An object of the present invention is to provide a fuel cell where a reactant gas can be supplied uniformly to a gas passage portion from a manifold portion despite that the manifold portion is offset from the gas passage portion.